FIGS. 17 and 18 show part of an aluminum plate for use in fabricating an aluminum layered heat exchanger for use as a conventional evaporator for motor vehicle coolers.
With reference to these drawings, the aluminum plate 40 conventionally has formed in one surface thereof front and rear fluid channel forming recessed portions 42a, 42b divided by a vertically elongated partition ridge 41, front and rear upper tank forming recessed portions 43a, 43b continuous with the upper ends of these portions 42a, 42b and having a larger depth than these portions, and front and rear lower tank forming recessed portions (not shown) continuous with the lower ends of these portions 42a, 42b and having a larger depth than these portions. The front and rear upper tank forming recessed portions 43a, 43b have respective fluid passage apertures 44a, 44b formed in their bottom wall. The front and rear lower tank forming recessed portions (not shown) have respective fluid passage apertures formed in their bottom wall.
Two adjacent aluminum plates 40, 40 are fitted together in superposed layers with their recessed surfaces opposed to each other to join the opposed partition ridges 41, 41 of the aluminum plates 40, 40 to each other and to join opposed peripheral edges 45, 45 thereof to each other, whereby a flat tube portion is formed which has front and rear flat channels, and front and rear upper tank portions, and front and rear lower tank portions continuous with the channel portions. Many such flat tube portions are arranged in parallel to cause the front upper tank portions of the adjacent parallel tube portions to communicate with each other, the rear upper tank portions thereof to communicate with each other, the front lower tank portions thereof to communicate with each other, and the rear lower tank portions thereof to communicate with each other.
To improve the heat exchanger in heat exchange efficiency, the refrigerant circuit is so designed as to cause the refrigerant to flow zigzag through the entire core of the exchanger. For this purpose, the assembly of many flat tube portions is divided into flat tube blocks. The refrigerant circuit has turn portions provided in one of the blocks for changing the direction of flow of the refrigerant from one side of each flat tube portion thereof to the other side, for example, from the front upper tank portion to the rear upper tank portion. The turn portion comprises a communication portion 50 for holding the front and rear upper tank forming recessed portions 43a, 43b of the aluminum plate 40 in communication with each other. A refrigerant flow direction changing passage is formed by the communication portions 50, 50 which are opposed to each other when the adjacent aluminum plates 40, 40 are fitted and joined to each other with their recessed surfaces opposed to each other.
With the conventional layered heat exchanger, however, the communication portion 50 for holding in communication the front and rear upper tank forming recessed portions 43a, 43b of the aluminum plate 40 has a bottom plate 51 which is flush with the bottom walls 46, 46 of these, recessed portions 43a, 43a, and these portions 43a, 43b and the communication portion 50 have the same depth. This increases the capacity of the entire tank portion at the turn portion for changing the direction of flow of the refrigerant in the flat tube portion, with the result that the stress due to the internal pressure of the refrigerant concentrates on the tank side walls, especially on the upper and lower walls 52, 52 as indicated by arrows in FIG. 16. Thus the heat exchanger has the problem that the tank side walls are lower than the other portions in limit strength against the internal pressure of the refrigerant.
Especially in recent years, it has been urgently requested to provide a structure capable of effectively preventing the tank side walls from being broken by the stress concentration due to the internal pressure of the refrigerant acting on the turn portion, in view of the cost reduction achieved by a reduction in the thickness of the plates for fabricating the heat exchanger while ensuring the efficiency of the heat exchanger.
An object of the present invention is to meet the above request by overcoming the problem of the prior art and to provide a heat exchanger wherein the tank side walls at the turn portion for changing the direction of flow of the fluid can be given an increased limit strength against the internal pressure of the refrigerant to diminish the concentration of stress on the turn portion due to the fluid internal pressure, give the turn portion sufficient resistance to pressure and effectively prevent the tank side walls from breaking, consequently making it possible to decrease the thickness of the plates for fabricating the heat exchanger, to assure the exchanger of a high efficiency and to achieve a cost reduction by the decreased thickness of metal plates.